1. Field of the Invention
The present invention relates to an over-voltage protection device. In particular, this invention relates to a circuit device that restrains the spike voltage and protects the over-voltage for a power adapter or a hand-held device.
2. Description of the Related Art
Reference is made to FIG. 1. When an electric equipment 20 (such as a laptop or a LCD etc.) that operates in DC power is providing power from an AC power, a power adapter 21 is required to convert the AC power into DC power. In FIG. 1, power adapter 21 obtains the AC power from an AC power plug 22, and converts the AC power into DC power for electric equipment 20. The structure in FIG. 1 has a problem. When electric equipment 20 is turned on or AC power plug 22 of power adapter 21 is plugged into the AC power socket (not shown in the figure), a large spike voltage easily occurs to generate spike current. The large spike current makes the AC power socket and the switch generate a spark or interfere with other electric equipments. The power quality is affected.
Moreover, when the AC power received by power adapter 21 is unstable (such as when the voltage is too high), power adapter 21 converts the over-voltage into over-voltage DC power, and delivers the over-voltage DC power to electric equipment 20. The over-voltage DC power will burn down electric equipment 20. Therefore, power adapter 20 needs a spike voltage restraining circuit and an over-voltage protection circuit to overcome the above problems.